Phonegap height change in IOS?

Phonegap height change in IOS?

I have a simple phonegap project, i want to add admobs to it, i need to
decrees the phonegap height to leave a 50dp space in the top of the
screen, and leave 90dp when on ipad, im not sure about the way to do this,
right now i just left a 50dp space in the html file where i place admob to
the top of the screen above that html, im sure this is not the right way
if i want to use smart banners for Iphones and ipads.
i trying doing some changes with this code but with no luck, im sure there
is another way.
CGRect screenBounds = [[UIScreen mainScreen] bounds];
self.window = [[[UIWindow alloc] initWithFrame:screenBounds] autorelease];